Lightweight paper stripping from a fuser roll is a recurring mode of failure in most fusing subsystems. Instead of the paper exiting the fusing subsystem it remains attached to the fuser roll, and results in a machine/roll failure. Many devices are currently in use to extend fuser roll life and facilitate lightweight paper stripping, including creep-based nip-forming fuser rolls (as described in U.S. Pat. No. 6,795,677 to Berkes et al. for High Speed Heat and Pressure Belt Fuser, hereby incorporated by reference in its entirety), stripping fingers, oiling subsystems and air knives. All of these devices are so called ‘dumb’ systems, operating in a standalone manner.
U.S. Pat. No. 5,406,363 to Siegel et al. for a “PREDICTIVE FUSER MISSTRIP AVOIDANCE SYSTEM AND METHOD,” discloses the use of feed-forward information (e.g., paper weight, image type, humidity, etc.) to predict the likelihood of fuser mis-strips and also claims compensation techniques—for example, increasing oil rate or increasing stripping force (air knife pressure or contact force)—that can be employed to reduce the number of failures.
Fuser stripping failures are significant because, first of all, any stripping failure requires the customer to open the fuser to remove jammed paper. This paper, which can contain un-fused toner, is often wrapped around extremely hot surfaces and pinched between high-pressure nips, making removal difficult. Second, stripping failures can significantly reduce the life of the fuser itself. In a contact-stripping system, high forces produced by a stripping failure often permanently damage the fusing member (e.g.: stripper-finger gouging of roll surface). In non-contact stripping systems mis-strips result in extended contact times between the reactive toner and the reactive fusing surface, often dramatically decreasing the chemical release life of these systems. Avoiding stripping failures requires aggressive stripping devices such as high-pressure air knives or high-load stripping fingers, which may cause other failures. Another alternative solution is to limit the machine to printing non-stressful papers and/or images.
From a strategic perspective, the need to avoid stripping failures places enormous constraints on fuser design and often leads to performance tradeoffs. For example, some production print systems employ fusers that require an undesirable lead-edge bleed (8 mm in size), or limit the usable substrates to only papers with greater than 80 gsm.
One of the solutions proposed herein is to monitor the performance of a fuser in-situ, using any of a number of diagnostic techniques and methods, and then using that information as feedback to warn a customer of impending failure, or to adjust the printed image or paper to avoid stripping failure. Such a solution would likely allow continued operation, albeit possibly with some deterioration in the system operation. A monitoring method and system disclosed herein allows in-line monitoring of stripping forces and post-fuser paper trajectories, leading toward prediction of fuser roll life and warning of imminent stripping failures. A sensor based control system, like that disclosed herein, would be able to monitor stripping performance and engage stripping facilitators in a ‘smart’ manner.
In xerographic production printing systems, such as the Xerox iGen production printer, fusing architectures often employ sensors that straddle the fusing nip—a paper entrance sensor and paper exit sensor. The known use of such sensors has been for jam detection, but it is presently recognized that such sensors can also be used for other purposes, such as timing of sheet passage through the fuser. For example, when the stripping subsystem is operating optimally, paper takes the shortest path between the two sensors, and thus the shortest time. As stripping performance degrades, however, the paper releases from the fusing roll at angles further and further from the centerline of the nip. This action likely generates paper pathlines that are no longer a straight line, but instead follow curved trajectories from the paper release point until the acquisition by the exit transport. The longer the pathline, the greater the time between the sensors detection of the paper. As described in more detail below, this is one method of monitoring the stripping performance of the system, either to provide early warning of failure, or to adjust a stripping facilitator.
A difficulty also exists in quantitatively predicting stripping performance of a color fuser, either initially or with degradation over the fuser's life, and of stripping life, either by print number or time. Hence, it is not unusual to observe order-of-magnitude differences in chemical release life and stripping life for fusers and their components. Moreover, expectations are low that a purely feed-forward solution can be achieved for most color fusers (albeit acknowledging that B/W systems might be substantially better behaved).
The systems and methods disclosed herein are part of a technique or strategy surrounding the use of in-line stripping sensors downstream of a fuser, combined with potential feedback control of various fuser/imaging parameters. Accordingly, another embodiment is directed to the use of post-fuser exit paper-path components, such as a dedicated finger or existing baffle, outfitted with multiple strain gauges. When used with diagnostic techniques described herein, such an embodiment can unobtrusively measure both the paper stripping forces and the paper exit trajectory, in contact or non-contact stripping systems.
Detecting or sensing characteristics of the paper exit trajectory allows one to monitor fuser roll stripping performance and predict imminent fuser roll failure. The post-fuser paper trajectory is an indicator for stripping performance because, as performance degrades, the paper remains attached to the roll for longer and longer times. As described above, this increases the distance of the paper release point from the centerline of the fusing nip, changing the angle between the paper's lead edge and, typically, horizontal. The change in this angle changes the paper's initial trajectory and ultimate path line. As both stripping force and exit trajectory are demonstrated to be strong predictors of impending stripping failure and fuser roll end-of-life, this embodiment may be used to further improve the monitoring of stripping performance in association with a fuser or similar subsystem in a paper path.
Techniques to resolve all or part of the substrate's pathline further include, but are not limited to: measuring the release point/angle; measuring the lead edge height at various locations; measuring multiple edge heights on a single sheet at a single location; monitoring the proximity of the sheet to an object in the post nip geometry; and measuring the distance from the fusing nip that the paper's lead edge engages the exit baffle/transport.
Disclosed in embodiments herein is a method for monitoring stripping performance in a substrate nip, comprising: detecting at least one characteristic indicative of the separation of a substrate from the nip and generating and representing the at least one characteristic; and adjusting, in response to the signal, at least one of a plurality of parameters related to the substrate nip to alter the at least one characteristic indicative of the separation of the substrate.
Also disclosed in embodiments herein is a method for monitoring stripping performance of a fuser in a xerographic printing machine, comprising: detecting at least one characteristic indicative of the separation of a substrate from the fuser and generating a signal indicative thereof; and adjusting, in response to the signal, at least one of a plurality of parameters related to the fuser to alter the at least one characteristic indicative of the separation of the substrate.
Further disclosed in embodiments herein is a printing system in which a toner image is fused to a substrate sheet in a fuser, comprising: a sensor for monitoring at least one of a plurality of parameters indicating separation of the sheet from the fuser and generating a signal indicative thereof; and a controller, responsive to the signal, for adjusting at least one of a plurality of parameters effecting separation of the sheet from the fuser.